title: Dosimetric analysis of imaging changes following pulmonary stereotactic body radiation therapy.
abstract: BACKGROUND
  The aim of this study was to determine whether late patterns of pulmonary fibrosis are related to specific radiation doses administered during thoracic stereotactic body radiation therapy (SBRT).
  
  
  METHODS
  The records of all patients treated with SBRT for either pulmonary metastases or inoperable primary lung tumours at the University of Alabama at Birmingham from November 2005 to July 2008 were reviewed. Patients selected for analysis had diagnostic chest computed tomography (CT) scans acquired at least 180 days after completion of therapy. CT scans acquired at follow-up were co-registered with the original treatment planning CT scans for 12 eligible patients (17 lesions), and late-occurring pulmonary imaging abnormalities (IAs) were contoured. Dosimetric parameters analysed include D(80) , D(90) , V(18) and V(prescription dose) of the IA and V(14) and V(18) of the lung.
  
  
  RESULTS
  Late pulmonary IAs were identified in 11 treated areas from nine patients. Late IAs could not be identified in six treated areas from three patients secondary to emphysema, tumour progression and severe atelectasis, respectively. The mean doses to 80% (D(80) ) and 90% (D(90) ) of the IAs were 18.4 and 14.5 Gy, respectively (ranges: 5.6-27.8 and 3.3-22.4 Gy). On average, 79.4% (range: 45.6-97.5%) of the IA received at least 18 Gy, while an average of 19.3% (range: 0.2-42.2%) received the prescription dose. On average, only 4.2% (range: 1.1-7.8%) of the lungs received 18 Gy.
  
  
  CONCLUSIONS
  Imaging abnormalities consistent with pulmonary fibrosis are common after SBRT and are well approximated by the 18 Gy isodose distribution. The clinical ramification of these findings should be evaluated in future studies.
authors.affiliation: Department of Radiation Oncology Thoracic Surgery, University of Alabama, Birmingham, Alabama, USA.
authors.forename: Brendan M
authors.initials: BM
authors.lastname: Prendergast
authors.forename: James A
authors.initials: JA
authors.lastname: Bonner
authors.forename: Richard A
authors.initials: RA
authors.lastname: Popple
authors.forename: Sharon A
authors.initials: SA
authors.lastname: Spencer
authors.forename: John B
authors.initials: JB
authors.lastname: Fiveash
authors.forename: Kimberly S
authors.initials: KS
authors.lastname: Keene
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Cerfolio
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: Minnich
authors.forename: Michael C
authors.initials: MC
authors.lastname: Dobelbower
mesh_terms: D000407:Alabama / Q000453:epidemiology; D015897:Comorbidity; D005260:Female; D006801:Humans; D015994:Incidence; D008175:Lung Neoplasms / Q000453:epidemiology* / Q000532:radiotherapy*; D008297:Male; D011658:Pulmonary Fibrosis / Q000453:epidemiology*; D011829:Radiation Dosage; D011832:Radiation Injuries / Q000453:epidemiology*; D011874:Radiometry / Q000706:statistics & numerical data*; D016634:Radiosurgery / Q000706:statistics & numerical data*; D018570:Risk Assessment; D012307:Risk Factors